1. Field of the Invention
The present invention concerns an insulative material surface coating. To be more precise, the invention concerns a surface coating for insulative material parts designed to assure protection against electromagnetic interference in a corrosive environment.
Said insulative materials include polymer materials and composite materials of the type including, for example, but not exclusively, a resin based on polymer material with reinforcing fibers.
One application of the present invention is the production of electromagnetic shielding for electrical or electronic component cases made of polymer or composite materials. The invention is therefore equally concerned with such shielded polymer or composite material cases for electrical or electronic components.
Another application of the present invention is the production of a protective layer, for parts subjected to severe constraints such as corrosion, that necessitates the presence of a metal protective layer having high adhesion, regardless of the external constraints.
2. Description of the Prior Art
Industrial processes for metalizing polymer material parts, in particular the so-called "wet" process and the so-called "vacuum evaporation" process, and the application of paint charged with metal particles are already known in themselves.
The wet process generally consists in appropriately preparing the surface, including steps of satin finishing and activation, followed by depositing a layer of copper in two steps, the first using chemical conversion, the second using electrolysis.
The vacuum evaporation process, very widely used in the decorative arts, consists in applying a very thin film of metal, generally aluminum, to the part to be coated by evaporation in a vacuum. Because it is thin, this film is very fragile. For this reason it is often protected by a varnish.
In some cases, metalization is sometimes preceded by an activation treatment using an atmospheric plasma or in a vacuum.
Finally, conductive paints, consisting of resins containing metal, for example copper, aluminum, silver, etc particles are sometimes used but have high resistivities and the thickness of the coating is not controlled with great accuracy.
Technical advances and ever more demanding performance requirements means that the current solutions have reached their limits and cannot be used in many cases.
In particular, new applications of electronics are leading to the use of portable equipment in more and more varied conditions, in particular outside buildings, introducing a new constraint, namely resistance to various forms of corrosion. This phenomenon can deteriorate or even destroy the metal layer, as in the case of aluminum and copper, and can also deteriorate the interface between the polymer substrate and the metal coating leading to partial or total detachment of the latter. In both cases, the electromagnetic protection of the components is no longer assured.
An object of the present invention is to provide a surface coating which, whilst having excellent adhesion to plastics and composite materials, together with remarkable resistance to corrosion, especially saline corrosion, provides high quality protection against electromagnetic interference and the adhesion of which is not affected by exposure to a corrosive atmosphere.
The Applicant has developed a surface coating composition for an insulative material substrate satisfying the above object by assuring durable electromagnetic protection, even in corrosive atmospheres.